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Is the equation Pressure = P(atmosphere) + (density(water).hight.gravity) correct? Or does that apply only for the pressure aplied on the bottom of the system?

(I'm sorry about the bad english)

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In summary, the conversation is about calculating the pressure exerted by a certain amount of water on the wall of a dam. The equation Pressure = P(atmosphere) + (density(water).height.gravity) is correct for finding the pressure at a certain depth, and it varies linearly. The force on the wall can be calculated by integrating the pressure distribution or by finding the area of the triangle. The atmospheric pressure can be left out as it acts on both sides of the dam and cancels out. The pressure at the bottom is equal to the pressure at the top, and the average pressure can be found by dividing the bottom pressure by 2. The correct formula for the pressure at a certain depth is P = (density

- #1

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Is the equation Pressure = P(atmosphere) + (density(water).hight.gravity) correct? Or does that apply only for the pressure aplied on the bottom of the system?

(I'm sorry about the bad english)

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- #2

Mentor

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That equation is correct. Realize that "height" is really *depth *below the water surface.

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- #4

Science Advisor

Homework Helper

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(the force sideways is the same as the force downwards because it is a fluid, so pushes in all directions)

Cyrus's reply is about calculating the TOTAL force on the wall.

At the bottom is the pressure you calculated, at the surface there is obviously no pressure and half way down is half the pressure.

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Cyrus said:

How do I do that, I mean, calculate it through the area of the triangle? (I rather do anything than integrate!)

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I calculated the pressure through that formula and then divided it by 2 and multiplied it by the area... and the result is correct... But I thought I had to use the atmospheric pressure in the formula...

Or is this pure luck?

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I calculated the pressure = 1000 (the density) x 40 (the height) x 9,8 (the aceleration of gravity. The result is 392000, which I divided by 2 = 196000. I multiplied this value by the area of the dem in contact with the water, 6000m2. The result is 1,176x10^9.

This was the result I was looking for.

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Yes that exactly right. Do you know what you are doing though?

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(I'm really sorry about the grammar errors, but I'm Portuguese, so there are some words and expressions I don't fully know how to spell or use)

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Science Advisor

Education Advisor

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You can leave out the atmospheric pressure because it is applied to the downstream side of the dam also - hence it cancels out. If there were no water in the lake at all, just the air on both sides, there would be no net force on the dam.

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MartaBraga said:

(I'm really sorry about the grammar errors, but I'm Portuguese, so there are some words and expressions I don't fully know how to spell or use)

Hint: The area of a triangle is 1/2*(base)*(height)!

To calculate the pressure of water, you will need to know the density of water, which is 1000 kg/m3, and the depth of the water. Use the formula P = ρgh, where P is the pressure, ρ is the density, g is the acceleration due to gravity (9.8 m/s2), and h is the depth of the water in meters.

The unit commonly used to measure water pressure is Pascal (Pa), which is equivalent to one Newton per square meter (N/m2). Other units that may be used include pounds per square inch (psi) and kilopascal (kPa).

The amount of water does not directly affect the pressure. The pressure is determined by the depth of the water and the gravitational force acting on it. However, the volume of water can indirectly affect the pressure if it changes the depth or shape of the water body.

Yes, the temperature of water can affect its pressure. As water warms, it expands and becomes less dense, which can lead to a decrease in pressure. On the other hand, as water cools, it contracts and becomes more dense, which can result in an increase in pressure.

Yes, you can calculate the pressure of water in a closed container using the same formula as before, but with the addition of the atmospheric pressure. The formula will be P = ρgh + Patm, where Patm is the atmospheric pressure. Atmospheric pressure can vary, but it is typically around 1013 hPa or 14.7 psi at sea level.

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